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Oak killing mold spreads in East Bay

The tiny culprit behind a deadly oak disease has spread in the East Bay and appears to have crept closer to residential areas in parts of Oakland and Berkeley, according to the latest survey.

"It may be an early warning sign," said Matteo Garbelotto, who heads UC's Forest Pathology and Mycology Laboratory.

Whether it was the rainy weather or the fact that surveys this year were much more intensive than previous years, it appears that the funguslike pathogen that causes sudden oak death is showing up more frequently at lower elevations in the Oakland hills. That means it could further spread next year, particularly if we have another wet winter, Garbelotto said.

"The jump was higher than we expected," Garbelotto said.

Sudden oak death, which has killed millions of trees along the Northern California coast since it was first detected about a decade ago, is established in several of the East Bay Regional Park District's properties in the hills. But the disease remains patchy there and has not spread as aggressively as it has in infected areas closer to the ocean.

But the latest survey results show for the first time that the pathogen is much more widespread in the East Bay.

"We're still looking at what is likely the early stage," Garbelotto said.

Sudden oak death has not been a major threat for East Bay homeowners, since most of the infections have been in more forested areas. But if it takes hold in residential areas it could force homeowners to consider expensive treatment options or other measures.

"It's not going to happen everywhere, but locally it may become a problem," Garbelotto said.

One of the volunteers who collected infected samples this spring in Dimond Canyon near Joaquin Miller Park in Oakland, signed on because two large oaks anchor the hillside on which her house sits.

"I asked an engineer and he said it's $50,000 to shore up the hillside if those oaks go," said Kathleen Harris, who lives slightly more than a mile from the infected bay laurel tree she found. "I'm very interested in sudden oak death prevention."

The infected tree Harris found is in a redwood-studded canyon and is one of three positive samples found west of Highway 13.

Sudden oak death was first noticed in the mid- to late-1990s with large numbers of tanoaks dying in Marin and Santa Cruz counties.

It was given its name in 2000 after majestic oaks were found dying and scientists identified the cause of the disease -- a previously unknown water mold they named Phytophthora ramorum.

Researchers feared it would devastate large swaths of coastal oak woodlands, but so far the spread has not been as bad as initially thought. Still, Garbelotto said the pathogen has spread through about 10 percent of its potential range in California, meaning it could become more much widespread.

"It is better to be prepared and cautious and assume the epidemic can reach its highest levels, rather than assume nothing is going to happen and be wrong," Garbelotto said.

It favors cool, moist and foggy climates and is less common east of the Oakland hills, though it has been found in Orinda, Moraga and in Briones Regional Park, said Brice McPherson, an associate specialist at UC's department of Environmental Science, Policy & Management.

Last spring's volunteer survey was the largest since it began in 2008, with nearly 500 volunteers collecting 10,000 samples from 2,000 trees from Humboldt County to Carmel.

Bay laurels spread the disease but are not killed by it. Finding infected bay laurels is a sign that the disease could appear in surrounding oaks or other trees, which is why the volunteer survey focuses on bay laurels.

The survey turned up "epidemic" levels of the mold along Skyline Boulevard in Los Gatos and Saratoga, and in general higher levels of infection than in previous years, which may be attributable to the wet year.

The only good news: there was no evidence the pathogen spread beyond a single infected tree in San Francisco's Presidio. "It's the first time we have a real extensive survey of the East Bay," Garbelotto said.

Sudden Oak death meeting:

Sausal Creek watershed area residents can learn more about sudden oak death treatment options and prevention at a meeting from 7 to 9 p.m. Nov. 16 at the Dimond Library, 3565 Fruitvale Ave. For information about the meeting, visit www.sausalcreek.org.